The field of the invention is magnetic tape recording and reproducing apparatus of the kind used in commercial broadcasting.
The National Association of Broadcasters Size A Cartridge has become the standard for the radio broadcasting industry, and is widely used in single capstan tape transport mechanisms. It has a rectangular plastic housing containing an endless tape trained along an apertured sidewall for movement successively as follows:
(a) From the inside of a rotatable storage roll around a stationary, upstream guide post; PA1 (b) past a first pressure pad which presses the tape against the curved face of a recording head; PA1 (c) around a stationary intermediate guide post; PA1 (d) past a second pressure pad which presses the tape against the curved face of a playback head; PA1 (e) between a capstan and pinch roller which are mounted on the tape transport mechanism; and PA1 (f) around a stationary, downstream guide post, to the outside of the rotatable storage roll.
This cartridge, although a great step forward when initially adopted, has a number of disadvantages for present day high precision broadcasting requirements as follows:
(1) The upstream, intermediate, and downstream guideposts are all integral parts of the molded plastics case. Being of plastics material, and being subject to warping with the case, they cause tape skew, and phase error in stereo recording and reproducing.
(2) The pressure pads are supposed to conform the tape to 5.degree.-7.degree. approach and departure angles as it passes the heads, but this is not absolutely uniform due to the fact that the pads are made of resilient, cellular, elastomeric materials. Pressure, and approach and departure angles, are not precisely uniform on all tracks, and variations in sliding friction between the tape and pads can create a number of problems including phase errors and poor low frequency response.
(3) The presence of a pressure pad behind the tape opposite the playback head prevents the use of a shield at that same location. The absence of such a shield requires the use of a special playback head casing having tiny windows surrounding the pole pieces, to minimize the effect of the magnetic field of the drive motor on playback reproduction. Unfortunately, the close proximity of the window edges to the pole pieces causes resonance up to about 150 cycles per second, thereby providing still another cause for poor low frequency response.
In summary, standard single capstan type cartridges have a number of inherent disadvantages including one or more of the following: phase error in stereo, low frequency resonance, and poor low frequency response.